biker mike
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i think a real time experiment is required,,,, as it seems itll be the only way to solve the argument ......... ]
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Nicky Tesla
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I bet you really are steptoe with your holier than thow replys to everybody's posts.
Its you who doesnt have any concept of ohms law. You cannot grasp the concept that a resistor MUST have a current flowing through it for a voltage to exist across it, and that voltage, can be found by multiplying the current flowing through it by its own resistance.
AND can you also grasp the concept that what flows in the cpc also flows in the live conductor. So the 230v will be shared across the two conductors so this meens if you are still with me steptoe, that the cpc CANNOT REACH 230v
The current in the cpc before the fault occurs is 0A that is why it is at earth potential.
When the fault occurs there will be if you have any vision, be able to realise that the current MUST start from zero and rise at an alarming rate giving a graph of current verses resistance(which also rises during the fault) giving the voltage across the cpc.
This voltage wants to go way past 50v, but the characteristics of the mcb prevent it if the conditions of low cpc values are met.
So Steptoe stop being so arrogant and put some theory and maths down instead of your Im superior to you type answers you give everyone not just me.
Its you who doesnt have any concept of ohms law. You cannot grasp the concept that a resistor MUST have a current flowing through it for a voltage to exist across it, and that voltage, can be found by multiplying the current flowing through it by its own resistance.
AND can you also grasp the concept that what flows in the cpc also flows in the live conductor. So the 230v will be shared across the two conductors so this meens if you are still with me steptoe, that the cpc CANNOT REACH 230v
The current in the cpc before the fault occurs is 0A that is why it is at earth potential.
When the fault occurs there will be if you have any vision, be able to realise that the current MUST start from zero and rise at an alarming rate giving a graph of current verses resistance(which also rises during the fault) giving the voltage across the cpc.
This voltage wants to go way past 50v, but the characteristics of the mcb prevent it if the conditions of low cpc values are met.
So Steptoe stop being so arrogant and put some theory and maths down instead of your Im superior to you type answers you give everyone not just me.
well there is someone on this thread that 'KNOWS' it will only be 50v MAX,i think a real time experiment is required,,,, as it seems itll be the only way to solve the argument ......... ]
if I was that way inclined(read stoopid) then Id do it,
but I think that man there has just volunteered....
step forward young man,
and welcome NICKY
round of applause peeps,,,,
B)
Nicky Tesla
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Go and buy a trailer load of old false teeth or something. ALBERRRRRT
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Welcome Nicky.
Nothing wrong with a "Healthy Argument".
Nothing wrong with a "Healthy Argument".
until you realise your rubbish isnt being taken in by anyone cos most of the peeps here actually understand the principles of wiring, and earthing arrangements.
Nicky Tesla
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Thats right constructive criticism yes bring it on, but sheer arrogance no
so Nicky,
Im sorry if I have missed something here,
but you have had this arrogance about being right with your postings about exporting an earth from a PME system,
yet you have failed to come up with any verifiable explanation as to how it would be safe to do so.
you have tried to state that under a phase earth fault condition that the cpc will not reach 230v potential,
that is just a ridiculous statement.
just how do you come about that conclusion?
that no prospective fault current capable of giving someone a severe electric shock will flow through an earth rod if you also connect to the MET of a PME system, yet your calcs are all wrong,
even though the fault current in PME could be up to 16kA, (DNO figure)
I have no idea how you can possibly even still consider making a dual earth system with TNCS and TT
or perhaps its the old scenario of a little knowledge is more dangerous than none at all.
Evenin` all.
Sorry I`m late. May I join in?
Nicky bud. Arrogance? I`ve just carefully read all postings since your first, and cannot honestly see ANY "out of order" comments from Steptoe or SL. Further, if my opinion is of any value, you have missed the basic premise of the indirect fault scenario; and I would suggest that if you were to back-track, and re-read the postings, you`ll find that these gents really DO know what they`re talking about. I`m not going to re-hash the argument within this post; as the topic has been comprehensively covered already.
Of course the EC/cpc rises towards Uo. No one suggests otherwise. But, although it won`t ever reach Uo; it could becove very (as in mV) close.
A PSC in excess of 10KA is not unheard of. As steptoe points out, DNO can, if determined by enquiry, quote 16KA as fault current.
You cannot work on the MCB`s rated figure. Otherwise, why would they be provided with a breaking figure (which is invariably in the KA realms)?
If the indirect fault, of negligable impedance, appeared on a 10mm T+E, 2M from the CU, in a domestic scenario (for arguments sake, lets call it TN-S).
2M 6mm cpc - approx 0.03 ohm (sorry, OSG in van)
Ze=0.01 ohm (measured)
IRRESPECTIVE of the overcurrent protective device.
I=V/R
=230/0.04=5700A
stop there a second, and confirm calculation.
Uo= phase/earth voltage=230V
R=0.01+0.03=0.04
ergo I=5750A.....ok so far?
That would be the current flowing (admittedly for a short duration, but we are talking instantaneous here, ok?)
Now lets introduce a parallel TT rod, which, due to the length of cable feeding it, has the following characteristics:
Rod impedance:99.87 ohms (allow for easy calcs. It`s late, and I`m tired.)
Earthing conductor impedance:0.1 ohm.
so we now have our two parallel resistances.
n.b. BOTH have Uo across them.
resistance 1: 0.04 ohms ( as described above)
resistance 2:
=0.03(cpc to CU)+0.1( 2nd E.C.)+99.87(Ra) =100 ohms
Yes........?
2 resistances in parallel. Voltage constant, current divides.
so fault current (5750A)/100.04 ohms=57.47 Amps
multiplied by 100(Ra)=2.29A
and by 0.04(R2+Ze)=5747A
Now, your comment r.e. resistors in series. You are correct. Lets look at that then, on the TT section:
0.03; 0.1; and 99.87 ohms respectively.
Series resistance - voltage divider.
Uo is still 230V
across a total of 100 ohms.
Uo per ohm =230/100=2.3
X 0.03 = 0.069V
X 0.1 = 0.23V
X 99.87 = 229.7V
All these are voltage across resistor.
So.... At the top of the rod, where connection is made, you will have Uo- 0.069 -0.23 =229.7
and at the bottom - You have the "general mass of earth".
If anyone sees a flaw in my description, please feel free to correct me. I would hope I know what I`m on about by now!!!
I really hope this helps; as I can`t think of a way to make it easier m8.
Nicky Tesla
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HOW ABOUT THINKING OF HOW YOU CALCULATE VOLT DROP TO STAY ABOVE 96%
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had writ me post & copied it in
then got this message...
:^O :^O:^O:^O:^O:^O:^O:^O:
I shall split it modiy and re-post in sections...
(a word at a time would catch biker mike an WW lol)B)
then got this message...
:^O :^O:^O:^O:^O:^O:^O:^O:I shall split it modiy and re-post in sections...
(a word at a time would catch biker mike an WW lol)B)
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Hi guys... HERE IS PART 1
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Hi guys...
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No ones shoutin m8 well I'm not anyway:^O:^O:^O
just need to make sure trainee sparks don't go thinking it is impossible to get hazardous voltages due to inappropriate earthin arrangements.
No i reckon smaller fonts are needed
get more on a page..
LOL
:^OStill watin to see your BUTT you keep promisin!
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I reckon thats about a week and a halfs worth of posts crammed into two posts!
Nicky Tesla
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LOOK IN THE REGS BOOKS AND GUIDES AND SEE HOW MANY GRAPHS AND CHARTS CONSIDER THE MCB BREAKING AMPS
I`m sorry - relevance to this scenario is?
NO THIS WILL BE THE CURRENT THE CONDITIONS WILL BE TRYING TO ACHIEVE...A CAR CANNOT GO FROM OMPH TO 100MPH AS IF IN A TIME WARP OR SOMETHING, IT WILL NEED TO ACCELERATE UP TO THAT SPEED, THE SAME PRINCIPLE HOLDS WITH THE FAULT CURRENT.
Maybe my explaination was at fault. I`m not talking about the instant that the fault occurs. A few milliseconds after will be fine.
so we now have our two parallel resistances.
WHERE? Cable sheath & TT rod
n.b. BOTH have Uo across them.
HOW DO THEY? Because there is a fault to earth of negligable impedance.
THE ONLY WAY 230V WOULD BE AT BOTH POINTS WOULD BE IF THERE WAS NO CURRENT FLOWING ...IE THE MET DISCONNECTED FROM EARTH
Sorry m8 - daft comment.
I think we are probably going to have to "agree to disagree" on this; unless SL`s in-depth & excellent posts have helped you understand.
SL - full marks on that. have that other scooby snack now m8
Nicky Tesla
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Nicky Tesla
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so we now have our two parallel resistances.
WHERE? Cable sheath & TT rod
CABLE SHEATH...WOT THE PVC ON THE OUTSIDE OF THE CABLE, THATS WOT THE SHEATH IS
IF YOU MEAN THE CABLE JOINING THE ROD TO THE MET, THEN THAT IS IN SERIES WITH THE ROD
WOT IS IN PARALLEL IS THE ROD AND THE MET (which has a distributors earth in these examples) JOIN THESE TOGETHER TO GET AN EQUIVALENT RES SLIGHTLY LOWER THAN THE ZE VALUE THEN CONNECT THE LOWER PART TO -VE (battery vision again) THE TOP PART TO THE BOTTOM OF THE NEXT RESISTOR BEING THE RESISTANCE FOR THE CPC (from the met to the fault) AND LASTLY THE TOP OF THAT RESISTOR WOULD BE JOINED TO THE +VE
TWO RESISTORS 1 ABOVE THE OTHER IN SERIES THATS SERIES AND ONCE MORE FOR GOOD LOOK IN SERIES, AND NOT SIDE BY SIDE IN PARALLEL
I
WHERE? Cable sheath & TT rod
CABLE SHEATH...WOT THE PVC ON THE OUTSIDE OF THE CABLE, THATS WOT THE SHEATH IS
IF YOU MEAN THE CABLE JOINING THE ROD TO THE MET, THEN THAT IS IN SERIES WITH THE ROD
WOT IS IN PARALLEL IS THE ROD AND THE MET (which has a distributors earth in these examples) JOIN THESE TOGETHER TO GET AN EQUIVALENT RES SLIGHTLY LOWER THAN THE ZE VALUE THEN CONNECT THE LOWER PART TO -VE (battery vision again) THE TOP PART TO THE BOTTOM OF THE NEXT RESISTOR BEING THE RESISTANCE FOR THE CPC (from the met to the fault) AND LASTLY THE TOP OF THAT RESISTOR WOULD BE JOINED TO THE +VE
TWO RESISTORS 1 ABOVE THE OTHER IN SERIES THATS SERIES AND ONCE MORE FOR GOOD LOOK IN SERIES, AND NOT SIDE BY SIDE IN PARALLEL
I
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